/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.http.server.reactive;

import java.util.function.BiFunction;

import org.reactivestreams.Publisher;

import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;

/**
 * {@link ServerHttpResponse} decorator for HTTP HEAD requests.
 *
 * @author Rossen Stoyanchev
 * @since 5.0
 */
public class HttpHeadResponseDecorator extends ServerHttpResponseDecorator {


    public HttpHeadResponseDecorator(ServerHttpResponse delegate) {
        super(delegate);
    }


    /**
     * Apply {@link Flux#reduce(Object, BiFunction) reduce} on the body, count
     * the number of bytes produced, release data buffers without writing, and
     * set the {@literal Content-Length} header.
     */
    @Override
    public final Mono<Void> writeWith(Publisher<? extends DataBuffer> body) {

        // After Reactor Netty #171 is fixed we can return without delegating

        return getDelegate().writeWith(
                Flux.from(body)
                        .reduce(0, (current, buffer) -> {
                            int next = current + buffer.readableByteCount();
                            DataBufferUtils.release(buffer);
                            return next;
                        })
                        .doOnNext(count -> getHeaders().setContentLength(count))
                        .then(Mono.empty()));
    }

    /**
     * Invoke {@link #setComplete()} without writing.
     *
     * <p>RFC 7302 allows HTTP HEAD response without content-length and it's not
     * something that can be computed on a streaming response.
     */
    @Override
    public final Mono<Void> writeAndFlushWith(Publisher<? extends Publisher<? extends DataBuffer>> body) {
        // Not feasible to count bytes on potentially streaming response.
        // RFC 7302 allows HEAD without content-length.
        return setComplete();
    }

}
